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An OSA Incubator Meeting explored the intersection of photonic technology and the effort to feed a growing world population.

The kinetics of degradation of RNA, total protein, ribosomal and soluble (R‐S) protein and DNA were followed over 24 hours in excised segments of Kentucky Wonder pole beans (Phaseolus vulgaris). In absence of exogenous auxin, RNA degradation proceeded from about zero time. By 15 hours, after about 20% of the RNA had degraded, the degradation of DNA, total protein and R‐S protein was initiated. Exogenous auxin (25 ppm α‐napthaleneacetic acid) prevented these degradations. The addition of kinetin had little or no effect. Auxin enhanced incorporation of orotic acid into RNA two to several times more than it did amino acids into protein. Actinomycin D repressed RNA synthesis about 75% including a repression of auxin‐induced synthesis. It had no effect on the basal level of protein synthesis but did repress auxin‐induced synthesis. The results indicate that the primary action of auxin in preventing senescence of bean endocarp tissue is at the site of RNA synthesis, and the effect of auxin on DNA and protein is a consequence of the effect of auxin on RNA metabolism.

We present a new method to obtain long-term stable phase-conjugate feedback (pcf) with a photorefractive crystal for a mode-locked semiconductor laser. The phase-conjugate mirror is a barium titanate crystal in a self-pumped internal reflection configuration, and the laser is a visible, antireflection-coated AlGaInP diode. We describe a new dynamic writing procedure for growth of an index grating in the photorefractive crystal that leads to stable pcf and discuss the reasons for this stability, which is the major advantage of this method over previously reported ones. Using this superior method, we achieve stable mode-locked operation of the laser with pulse widths of ∼30 ps and a timing jitter of less than 2 ps.

We demonstrate the application of a type II AlxGa_1−xAs/AlAs multiple quantum well as a fast saturable absorber in a hybridly mode-locked dye laser. Type II multiple quantum wells are promising for this application because of the fast recovery of the saturated absorption with picosecond or even subpicosecond time constants. We obtain almost transform-limited pulses as short as 0.9 psec for a type II sample with a recovery time of 2.3 psec.

The authors have investigated the stability of an external cavity laser diode modelocked by optoelectronic feedback. The measured picosecond pulses at repetition frequencies of up to 1.2 GHz exhibit an amplitude and phase jitter of the order of a few percent, increasing with increasing repetition frequency.

Time resolved polarisation characteristics of 1.3μm GaInAsP/InP-RW lasers are presented, showing the switching behaviour between the TE and TM mode as well as polarisation bistability. A switching time of about 50ps is observed for the transition between TE and TM polarisation under 900MHz current modulation. This is the shortest switching time measured so far.

It is demonstrated that mode locking of an external cavity GaAs/(GaAl)As semiconductor laser can be achieved by regenerative feedback of the amplified RF beats of the longitudinal modes detected by a fast photodetector. Stable pulse trains with 10 to 40 ps pulsewidth are generated by careful adjustment of DC bias, amplification of the electronic feedback and optoelectronic delay. Results are presented which explore the capability of this new mode locking technique for the generation of pulse codes for future OTDM systems.

We present a new concept for an electronically tunable diode laser. It is based on an external-cavity configuration with simultaneous feedback and intracavity spatial separation of the laser’s spectral components. The electronical tunability is achieved by insertion of a liquid-crystal array as an electronically controlled aperture into the region of spatial separation of the spectral components. Wavelength tunability without mechanical movement over a range of 10 nm and two-color operation are demonstrated with a 670-nm laser diode.

It is demonstrated that the lasing transition of a quantum well laser can be tailored to take place either between the n = 1 or n = 2 sub-band by proper design of the facet reflectivity. Facet reflectivity is controlled by monitoring the laser emission spectrum in situ during the deposition of antireflection (AR) coating.

IT has been shown1,2that auxins delay the onset of senescence in bean endocarp and various leaf tissues (Rhoeo, Mesembryanthemum) maintained in vitro. In the absence of auxin, liquid-logging of intercellular spaces is followed by cellular dissociation and rounding off of cells. Similar changes have been observed in the abscission zones of Coleus, Cestrum and Fuchsia. When de-seeded bean pod segments are maintained in Petri dishes on wet filter paper, liquid-logging is evident in 2½–3 days and an exudate appears on the upper tissue surfaces. Cellular dissociation is usually complete by the fifth day. These changes are essentially prevented by the addition of an auxin (3-indoleacetic acid or α-naphtha-leneacetic acid) to the culture medium. There are no significant differences in increase in fresh weight or respiratory activity between water- and auxin-treated endocarp segments over a ten-day period. The cells of liquid-logged segments are still capable of plasmolysis and deplasmolysis. The results indicate that the liquid-logging and exudation are manifestations of changes in permeability. A second process involves changes in the composition of the cell-wall cementing substances which take place in the absence of auxin and give rise to cellular dissociation and rounding off of cells.

The increase in RNase activity that occurs in fresh cut Rhoeo discolor leaf sections was followed in sections aged in water or deuterium oxide for 24 hr. The increase in RNase activity is probably due to de novo synthesis, since the buoyant density of the RNase from the deuterium labelled tissue was significantly higher (1.10 to 1.88%) than that of the controls.